From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AA385C2D0E4 for ; Tue, 17 Nov 2020 12:22:58 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 3DB04207D3 for ; Tue, 17 Nov 2020 12:22:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="dNB3EZOf" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3DB04207D3 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=ddLtXXalRDUDy74krrr81Stz9ysVuTiSz3L7nID/wOo=; b=dNB3EZOfnn7xLz+megrcZmVGK L23pd5dsoiJMocr2VkMuW6bT9otDJ0a5J1tNqNZ6gvj9hTkNsW7x8xkPaxpUor8RoancHosF63Q9/ papiSfAChOlY9W96jHMVnHjX1FWEtuvZCUfPMAawyCtA9bppVpClYCTVHCL5EUNzVeRZtuexi6tSl vvu6Z7Jw4xGm9dQAx2YQrt9C03j/lHUSN92h8/izlN6Z6ZjJsqTuwwAM2FAxF2GxB6zCeNLwJud2d XOMK6G7XBbWZzQXBFhNPptzy7tpiE11ZQaFibCjG1V12tDR1l7YD2O6NJ+RAfZ03KLjqeheqAQmZF meYowtmqw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kezzk-0003NX-H4; Tue, 17 Nov 2020 12:22:00 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1keykk-0008Bh-VS for linux-arm-kernel@lists.infradead.org; Tue, 17 Nov 2020 11:02:36 +0000 Received: from trantor (unknown [2.26.170.190]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 23BD5238E6; Tue, 17 Nov 2020 11:02:22 +0000 (UTC) Date: Tue, 17 Nov 2020 11:02:20 +0000 From: Catalin Marinas To: Mark Rutland Subject: Re: [PATCHv4 14/17] arm64: uaccess: remove set_fs() Message-ID: References: <20201113124937.20574-1-mark.rutland@arm.com> <20201113124937.20574-15-mark.rutland@arm.com> <20201117104454.GA73209@C02TD0UTHF1T.local> <20201117105740.GB73209@C02TD0UTHF1T.local> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201117105740.GB73209@C02TD0UTHF1T.local> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201117_060227_909476_7497ED6D X-CRM114-Status: GOOD ( 28.14 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: james.morse@arm.com, will@kernel.org, hch@lst.de, linux-arm-kernel@lists.infradead.org, robin.murphy@arm.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Nov 17, 2020 at 10:57:40AM +0000, Mark Rutland wrote: > On Tue, Nov 17, 2020 at 10:54:18AM +0000, Catalin Marinas wrote: > > On Tue, Nov 17, 2020 at 10:44:54AM +0000, Mark Rutland wrote: > > > On Mon, Nov 16, 2020 at 05:40:48PM +0000, Catalin Marinas wrote: > > > > On Fri, Nov 13, 2020 at 12:49:34PM +0000, Mark Rutland wrote: > > > > > We no longer need to flip UAO to access kernel memory under KERNEL_DS, > > > > > and head.S unconditionally clears UAO for all kernel configurations via > > > > > an ERET in init_kernel_el. Thus, we don't need to dynamically flip UAO, > > > > > nor do we need to context-switch it. However, we do need to clear UAO > > > > > (and set PAN) during SDEI entry. > > > > > > > > If the kernel never sets the UAO bit, why do we need to clear it during > > > > SDEI entry? > > > > > > The fear was taking an SDEI event from a VM which had UAO set, with the > > > SDEI FW not clearing UAO. > > > > > > That might not happen in practice because while the spec implies that > > > could happen, TF-A currently generates a new PSTATE from scratch, and > > > going forward the spec will be aligned with regular exception entry > > > rules for PSTATE (so UAO will be cleared automatically). > > > > Does this requirement apply retrospectively or it only for the future > > SDEI specs? > > It applies from the current spec, but note that TF-A has always > generated a new PSTATE (with UAO clear). And we can assume that TF-A is the only implementation generating SDEI. > > > So we can probably drop the clearing of UAO if you prefer. > > > > I don't like clearing UAO specifically. There may be other PSTATE bits > > in the future we don't know or care about and that are left set by > > firmware. If we don't trust firmware to give a clean PSTATE, can we > > reset it with an ERET? > > In future we should get the new behaviour, so I think we should be fine > there. If we can't trust PSTATE at all, then we're not necessarily able > to perform an ERET anyway. > > ... which I think means I'm arguing in favour of deleting the clearing > of UAO, if you're happy with that? Yes, I'm fine with that. That means that you can also get rid of cpu_has_uao(). Could we apply the same logic to SDEI+PAN? -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel